1. Field of the Invention
The present invention relates to the production of copper sheets and metal sheets and, in particular, to the use of wrought copper cathode starting sheets in the electrolytic production of copper in which the starting sheets are made by reducing cast copper to a wrought sheet form and preferably where a continuous casting process is used to make a continuous casting which is reduced in a rolling process to a starting sheet.
2. Description of the Related Art
Copper is produced by electrolytic processes such as electrorefining and electrowinning and, for convenience, the following description will be directed to electrorefining, although the products and processes of the invention are applicable to all electrolytic copper processes.
In one process, the electrorefining of copper comprises forming blister copper anodes by melting and casting individual anodes, followed by electrodepositing copper over a 1-2 week period onto pure copper starting sheets in electrolytic production cells from the impure anode. The pure copper cathode product is then melted and processed into the desired forms such as a wire bar, rod, billet, etc. It will be understood by those skilled in the art that the blister copper anodes contain about 98% copper and minor amounts of impurities, whereas pure (i.e. refined) copper electrodeposited either as a starting sheet or final product contains about 99.95% copper.
The copper cathode starting sheets are thin sheets of pure copper usually having a thickness of about 0.025 to 0.070 inch and have a width and length about that of a copper anode or cathode, i.e., 37 inch.times.40 inch. They are generally produced in special stripper cells by a 24-hour electrodeposition of copper onto a starter blank from an impure anode, usually called a stripper anode. The starter blank may be made of various metals, such as stainless steel and titanium, and the procedures of deposition are generally the same as in production cells to make pure copper cathode except for the daily withdrawal and stripping of the thin copper starting sheet deposit from the starter blank. The final preparation of the starting sheets may comprise stripping the copper from the blank, washing, straightening, stiffening and trimming to the desired size and attaching cut starter sheet loops for support in the production cell.
In another copper electrorefining process termed the ISA process, stainless steel sheets, like the starter blank used to make starting sheets, are used to plate copper thereon for typically seven days at which point the deposited copper is stripped and used to make copper products.
Unfortunately, however, the ISA process is expensive and the process requiring the preparation of starting sheets is inefficient and has been a continuing problem for the copper industry because the need for stainless steel sheets and the required high standards of quality for starting sheets result in high costs, both in labor and energy and time, and in a high scrap rate in the starter sheet process. For example, the starting sheet is generally of a fixed dimension limited by the size of the electrodeposition tank and it is industrially important that the stripper anode be of optimum size because of the high cost in energy and labor of making the anode and reprocessing of anode scrap remaining after electrodeposition. The anode however, must still provide substantially complete and even coverage over the starting blank and industry has had to correlate the anode size with the size of the starter blank and other process variables to minimize the cost of making starter sheets. U.S. Pat. No. 4,490,223, to Baldwin, provides a solution to the above problem by utilizing a specially designed footed stripper anode and this patent is hereby incorporated by reference. Starting sheets also because of their thinness and method of preparation (e.g., stripping of the sheet from the starter blanks) tend to warp or curl and not hang straight in the production cell causing contact with the anode and shorting and loss of electrical efficiency. In the ISA process, and in the copper starting sheet process, large inventories of stainless steel or other starter blank sheets must be used and inventoried which is expensive.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide copper cathode starting sheets which may be made efficiently and cost effectively.
A further object of the present invention is to provide wrought copper cathode starting sheets.
Another object of the present invention is to provide a method for the making of copper cathode starting sheets which have superior processing properties than electrodeposited starting sheets.
Other objects and advantages of the invention will in part be obvious and will in part be readily apparent from the specification.